Disposable diapers have met with increased commercial acceptance in recent years primarily because of their convenience, as opposed to cloth diapers, which need to be laundered once soiled. Many different constructions have been proposed and used, and some have met with widespread commercial success in spite of certain inadequacies in functional properties.
One of the most serious prior art problems has been the inability to provide a suitable construction that would keep moisture away from the surface of the diaper which comes into contact with the infant's skin and thereby avoid skin irritation and infection. Commonly assigned Mesek et. al. U.S. Pat. No. 3,612,055 discloses several diaper constructions that function extremely well in keeping moisture away from an infant's skin, while at the same time handling a full volume discharge of urine.
These functions are accomplished by a multilayer diaper comprising, in order, a fibrous facing layer which is to be brought into contact with the infant's skin, a layer of highly porous, loosely compacted cellulosic batt, a paper-like densified, highly compacted cellulosic fibrous layer integral with the loosely compacted batt and an impervious backing sheet adhered to the densified layer throughout the interface therebetween. The facing layer is of porous construction and its fibers have less wettability for water than the fibers of the loosely compacted batt, resulting in a tendency for liquid to flow from the facing web into the batt. The densified fibrous layer has a smaller average pore size than the loosely compacted batt, resulting in a tendency for liquid to flow preferentially from the batt into the underlying densified layer rather than to other areas of the batt, thus tending to restrict wetting in the batt to an area of moderate size. Liquid flowing into the densified layer tends to spread laterally because of its wicking action and liquid which might pass through the densified layer during discharge (when flow is rapid) is held back by the impervious backing sheet for sufficient time to permit absorption to take place. Liquid in excess of the absorptive capacity of the densified layer is forced back by the impervious layer into the dry portion of the loosely compacted batt, thus utilizing the additional absorptive capacity therein.
The above-mentioned patent discloses basically two different types of absorbent panels, viz., those wherein the paper-like, densified layer extends continuously over a given area of the loosely compacted batt, and those wherein the paper-like densified layer is discontinuous and arranged in a preselected geometric pattern. The advantage of the absorbent structures within the latter group is the ability to provide directionalized fluid flow, i.e., the fluid tends to flow in the direction of the densified portions, as opposed to flowing into the loosely compacted portions of the absorbent panel. Thus, by utilizing an absorbent panel wherein the spaced densified portions extend in a lengthwise direction, the fluid flows preferentially along the densified portions to spread out longitudinally within the densified layer before spreading laterally and striking through at the side edges thereof. While absorbent panels having spaced densified portions provide increased ability to control and direct the flow of fluid, as opposed to a continuous paper-like, densified layer wherein the fluid flow is substantially equal in all directions, such structures have a reduced volumetric fluid storage capacity in the densified portions and somewhat reduced overall structural integrity, as compared to comparable structures having a continuous paper-like densified layer. Furthermore, because the spaced densified portions of the panel are separated by loosely compacted batt portions having limited wickability, the linear flow rate in the densified portions is far greater than the rate of lateral spread, with the result that fluid often reaches the ends of the densified portions before it spreads outwardly into previously unwet portions of the absorbent structure. This, of course, can result in fluid leakage at the ends of the absorbent panel.
In absorbent panels including a continuous densified layer of uniform thickness, because of the equal flow rate in all directions, it is possible for fluid to migrate to the side edges of the densified layer before it reaches the longitudinal edges thereof, with resultant fluid leakage at the sides of the product. Thus, both types of absorbent panels disclosed in the above mentioned patent have certain limitations.
The above-mentioned patent also discloses an arrangement which provides for improved sealing adjacent the thighs of an infant. To this end, the patent teaches that the facing layer may be wider than the backing sheet, with the edges of the facing layer being folded inwardly to make the facing layer substantially coextensive in size with the backing sheet and to provide increased thickness at the marginal side portions of the diaper. This latter construction not only provides for improved sealing, but also enhances the balance and feel of the diaper.
While diapers with the facing layer folded in the manner described above have functioned satisfactorily to produce the desired results, since the facing layer is the most costly component of the diaper, the improved sealing effect and improved feel have been obtained as a result of an increased amount of facing layer material, beyond that which otherwise would be required, and this has resulted in an increase in the cost of manufacturing the product, a matter of no small importance in a disposable diaper.